The authors examined whether acute pulmonary embolism (APE) increases lung matrix metalloproteinase (MMP)-2 and MMP-9 activities and whether inhibition of MMPs with doxycycline attenuates the hemodynamic changes associated with APE. Anesthetized male Wistar rats were monitored for mean arterial blood pressure (MAP) and heart rate (HR). Rats in the control group (n = 5) received only saline IV; rats in the embolism (Emb) group (n = 8) received saline IV followed 10 minutes later by an injection of Sephadex microspheres (9 mg/kg) IV; rats in the doxycycline (Doxy) group (n = 4) received only doxycycline (30 mg/kg) IV, followed 10 minutes later by an injection of saline IV; rats in the Doxy + Emb group (n = 8) received the same dose of doxycycline followed 10 minutes later by the same amount of microspheres described above. Lung samples were homogenized and assayed by SDS-polyacrilamide gel electrophoresis gelatin zymography to evaluate lung MMP-2 and MMP-9 activities. Saline or doxycycline produced no significant changes in MAP, HR, and in MMP-2 and MMP-9 activities. Conversely, lung embolization significantly reduced MAP by > 32 mm Hg and HR by > 90 bpm for more than 60 minutes, and increased MMP-9 activity by 43% (all p < 0.05). No significant differences were observed in MMP-2 activity. However, lung embolization produced only transient hypotension in rats pretreated with doxycycline. In this group, MAP returned to baseline values 5 to 10 minutes after embolization. In addition, pretreatment with doxycycline blunted the increase in lung MMP-9 activity after lung embolization (p < 0.05). This study demonstrates for the first time that MMP-9 inhibition with doxycycline attenuates APE-induced hemodynamic changes in the animal model examined. These findings indicate that MMP-9 activation plays a role in the pathophysiology of APE and suggest that pharmacologic strategies targeting specific MMPs with selective inhibitors may prevent the detrimental acute hemodynamic consequences of APE.